1. Field of the Invention
The present invention relates to a printing apparatus that prints an image by transferring an ink image formed on an intermediate transfer member to a printing medium, and to a control method of that printing apparatus.
2. Description of the Related Art
An inkjet printing method using an inkjet ejection apparatus used widely by consumers is also used industrially, and its application is expected to increase even further. One of the application areas is the printing field. When such an inkjet printing method is applied to the field of printing, there is no need for a printing plate as was necessary in conventional printing methods such as offset printing, and because the lead time is extremely short, it is possible to quickly obtain the desired printed materials. These features are gaining attention as preferred technology for meeting the present needs of multiple products, small lots and short delivery time.
However, in an inkjet printing method that uses such an inkjet ejection apparatus, there is a possibility of a decrease in image quality due to certain unique phenomena. One of the phenomena is called the “bleeding” phenomenon and other one is called the “beading” phenomenon. Bleeding is a phenomenon in which when ink is directly applied to a printing medium such as paper having a flat smooth surface using an inkjet ejection apparatus, the ink is not completely absorbed by the paper and some remains on the surface of the paper, so adjacent inks that have been applied to the paper mix with each other. Beading is a phenomenon in which ink that is applied to the paper first is drawn in by ink that is applied to the paper later, which leads to the possibility of a decrease in the printing quality of the image and may cause poor drying of the paper.
In order to reduce such phenomena, a method has been proposed (transfer type inkjet printing method) in which an ink image is formed on an intermediate transfer member by the inkjet ejection apparatus, and that ink image is then transferred onto a printing medium. Moreover, a technique has been proposed in which in order to transfer an ink image that is on an intermediate transfer member to a printing medium without a decrease in the image quality, the intermediate transfer member is coated with a coating solution. This coating solution is generally called a reaction solution, with a reaction component that lowers the fluidity of the coloring material in the ink. When this reaction solution comes in contact with ink on the intermediate transfer member, the fluidity of the coloring material instantly decreases due to the function of the reaction component in the solution, and distortion of the ink image being suppressed.
However, in this kind of transfer type inkjet printing method, when images are printed continuously, the characteristics of the surface of the intermediate transfer member changes and the reaction solution ceases to perform its function properly. Such a situation may lead to distortion of the image and decrease in image quality. Therefore, it is necessary to periodically replace or recycle the intermediate transfer member, and it is preferable that the replacement period or the recycle period be appropriately set. That is because, when the replacement or recycle is performed too late, there is an increased possibility that images will be produced having poor image quality, and conversely, when the replacement or recycle is performed too early, the intermediate transfer member will be replaced unnecessarily, which is disadvantageous from the aspect of productivity and cost.
In Japanese Patent Laid-Open No. 2007-022082, a transfer surface maintenance system monitoring method is disclosed as a method of appropriately setting the replacement period for replacing the intermediate transfer member. In other words, first, an ink image of a test pattern is formed on the intermediate transfer member, and that ink image is captured by an image detector to acquire a printed pattern response. Next, using the transfer surface maintenance system, the intermediate transfer member is cleaned after which the image remaining on the intermediate transfer member is captured by the image detector to acquire a cleaned image response. The printed pattern response and cleaned image response are then compared to calculate the cleaning efficiency, and by comparing the calculated result with a specified limit, whether or not there is problem with the intermediate transfer member is determined. When it is determined that there is a problem with the intermediate transfer member, a correction process is executed.
The method disclosed in Japanese Patent Laid-Open No. 2007-022082 determines whether or not there is a problem with the intermediate transfer member by comparing the test pattern formed on the intermediate transfer member and the cleaned image response, and based on that information, sets the period for replacing or recycling the intermediate transfer member.
However, this method presumes that the surface of the intermediate transfer member when forming the test pattern is proper, so it is difficult to apply this method to a case in which the characteristics of the surface of the intermediate transfer member change greatly, and the test pattern cannot be formed properly. In addition, in this method, it is necessary to form a test pattern that cannot be used in production, and while forming that test pattern, there is a possibility that the original printing process will be disrupted. Furthermore, in this method, there is also a large problem in that it is not possible to detect the period for replacing or recycling the intermediate transfer member beforehand, so there is a possibility that images will be formed with poor image quality.